Taken from browserify-buffer.
Also adds a few more tests to assert this is working correctly from both
read and write perspectives.
The assertion in for writePushDataInt in the 32 bit case was
unnecessary as that is handled by buffer.writeUInt32LE anyway.
After a long IRC discussion, it was decided that the use of direct
filepaths instead of the module is a more pure form of testing ,
although it may provide less overall coverage than the mixed integration
style imports used previously.
This will need to be remedied by further integration testing in
/test/integration.
